Revista Chilena de Historia Natural 76 (3): 485-499, 2003
RESEARCH ARTICLE
Microbial mats from the Llamará salt flat, northern Chile
Stratified photosynthetic microbial mats are described from the Salar de Llamará, a salt
flat basin located in the Atacama desert of northern Chile. Microscopic and spectrophotometric techniques were used. The thickness
of the photic zone of these communities spans 8 to 30 mm. This is probably due to the grain size and mineralogical composition of
associated sediments. Three different types of mats were recognized. A first one was characterized by a green pigmented layer; a
second with orange and green coloured layers, and the third with orange and green layers and an additional purple layer. At one
sampling site, no pigmented layers were present. Sediments underlying the mats were white, but in one site, black coloured sediments
were observed; this dark colour is probably the result of iron sulphide precipitation. Predominant microorganisms in the orange
pigmented layers were diatoms and unicellular cyanobacteria, mainly from the Cyanothece and
Synechococcus groups. Filamentous cyanobacteria Microleus sp. and Oscillatoria sp. were the
most abundant in the green layer. When interstitial brines reached salinities between 12 and 33 %, no diatoms were observed, and the
coccoidal cyanobacteria from the Synechococcus, Cyanothece and Gloeocapsa groups and genus
Gloeobacter predominated over filamentous Cyanobacteria in the green layer. The purple layer was built primarily of
anoxygenic phototrophic bacteria similar to cells of the genera Chromatium and Thiocapsa. Absorption
spectra revealed that chlorophyll a is the most abundant pigment in most of analyzed samples. Integrated values of chlorophyll a and
bacteriochlorophyll a reached values of up to 230 and 144 mg m<sup>-2</sup> along all of the pigmented zone, respectively.
Abundant non-photosynthetic microorganisms were found in the mats, including unidentified cocci and bacilli. Sulphate reducing
bacteria were present in all the sampled mat.
Key words:
Chile, microbial mats,
salt flats, desert, phototrophic bacteria
